Lubricating oil compositions

ABSTRACT

A heavy duty diesel engine lubricating oil composition comprising, or made by admixing:  
     (A) a major amount of an oil of lubricating viscosity comprising at least 35 mass % of a Group III basestock, based on the mass of the oil of lubricating viscosity, that contains at most 0.03 mass % of sulfur, based on the mass of the basestock, and that has a viscosity index of 120 or greater and has greater than or equal to 90 mass % saturates, based on the mass of said basestock; and  
     (B) a minor amount of an additive composition comprising:  
     (i) a detergent composition; and  
     (ii) one or more other additives;  
     wherein the oil composition has a cold cranking simulated viscosity, measured according to ASTM D2602, of less than 7000 mPa.s at −25° C. and a sulfated ash, measured according to ASTM D874, of less than 1.35 mass %, based on the mass of the oil composition. The oil compositions provide improved piston cleanliness of a heavy duty diesel engine.

[0001] The present invention concerns lubricating oil compositions forlubricating the crankcase of engines, particularly compression-ignitedengines, such as heavy duty diesel engines, for example, engines foundin road trucks.

[0002] Lubrication of the crankcase of internal combustion engines isnecessary to maintain the performance and expected life-time of theengine, for example by keeping the engine as clean as possible.

[0003] The heavy duty trucking market employs the diesel engine as itspreferred power source due to its excellent longevity, and specialisedlubricants have been developed to meet the more stringent performancerequirements of such heavy duty diesel engines than passenger carengines.

[0004] It has been found that viscous lubricating oil compositions tendto provide better engine cleanliness than less viscous lubricating oilcompositions: this is particularly evident in the OM441LA engine test,where piston cleanliness is assessed on two grooves on the piston.

[0005] A potential means of improving the cleanliness effect of oilcompositions is to include detergent additives, such as calcium ormagnesium sulfonate and phenate, which are believed to improve enginecleanliness. However, regulations aimed at reducing environmentalpollution caused by exhaust gas components, such as particulates andnitrogen oxides (NO_(x)), are driving lubricating oil compositions tolower sulfated ash, and therefore, to a reduced amount of detergents.This is because metal-containing additives, such as metal detergents,zinc compounds and molybdenum compounds, contribute to the amount ofsulfated ash.

[0006] It has been surprisingly found that satisfactory pistoncleanliness can be achieved for lubricating oil compositions that areless viscous and contain a reduced amount of detergent additives.

[0007] Accordingly, in a first aspect, the present invention provides aheavy duty diesel engine lubricating oil composition comprising, or madeby admixing:

[0008] (A) a major amount of an oil of lubricating viscosity comprisingat least 35 mass % of a Group III basestock, based on the mass of theoil of lubricating viscosity, that contains at most 0.03 mass % ofsulfur, based on the mass of said basestock, and that has a viscosityindex of 120 or greater and has greater than or equal to 90 mass %saturates, based on the mass of said basestock; and

[0009] (B) a minor amount of an additive composition comprising:

[0010] (i) a detergent composition; and

[0011] (ii) one or more other additives;

[0012] wherein the oil composition has a cold cranking simulatedviscosity, measured according to ASTM D2602, of less than 7000 mPa.s at−25° C. and a sulfated ash, measured according to ASTM D874, of lessthan 1.35 mass %, based on the mass of the oil composition.

[0013] In a second aspect, the present invention provides a method oflubricating a heavy duty diesel engine, which engine has a totaldisplacement of at least 6.5 litres and a displacement per cylinder ofat least 1.0 litre per cylinder, which method comprises supplying to theengine a lubricating oil composition as defined in the first aspect.

[0014] In a third aspect, the present invention provides a combinationof a heavy duty diesel engine, which engine has a total displacement ofat least 6.5 litres and a displacement per cylinder of at least 1.0litre per cylinder and a lubricating oil composition as defined in thefirst aspect.

[0015] In a fourth aspect, the present invention provides the use of anoil of lubricating viscosity comprising at least 35 mass % of a GroupIII basestock, based on the mass of the oil of lubricating viscosity,that contains at most 0.03 mass % of sulfur, based on the mass of saidbasestock, and that has a viscosity index of 120 or greater and hasgreater than or equal to 90 mass % saturates, based on the mass of saidbasestock, in a lubricating oil composition for improving the pistoncleanliness of an engine.

[0016] In a fifth aspect, the present invention provides a method ofimproving the piston cleanliness of an engine, particularly in theOM441LA test, by adding to the engine a lubricating oil composition asdefined in the first aspect.

[0017] In a sixth aspect, the present invention provides a heavy dutydiesel engine lubricating oil composition giving at least 25 pistoncleanliness merit points and not greater than 4% boost pressure loss inthe OM441LA engine test, according to the CEC-L-52-T-97 procedure, whichoil composition comprises, or is made by admixing:

[0018] (A) a major amount of an oil of lubricating viscosity; and

[0019] (B) a minor amount of an additive composition comprising

[0020] (i) a detergent composition; and

[0021] (ii) one or more other additives;

[0022] wherein the oil composition has a cold cranking simulatedviscosity, measured according to ASTM D2602, of less than 7000 mPa.s at−25° C. and a sulfated ash, measured according to ASTM D874, of lessthan 1.35 mass %, based on the mass of the oil composition.

[0023] In this specification:

[0024] “Major amount” means in excess of 50 mass % of the composition.

[0025] “Minor amount” means less than 50 mass % of the composition, bothin respect of the stated additive and in respect of the total mass % ofall of the additives present in the composition, reckoned as activeingredient of the additive or additives.

[0026] “Comprises or comprising” or cognate words are taken to specifythe presence of stated features, steps, integers, or components, but donot preclude the presence or addition of one or more other features,steps, integers, components or groups thereof. In the instance the term“comprising” or comprises” is used herein, the term “consistingessentially of” and its cognate are within its scope and are a preferredembodiment of it, and consequently the term “consisting of” and itscognate are within the scope of “consisting essentially of” and are apreferred embodiment of it.

[0027] “TBN” is Total Base Number as measured by ASTM D2896.

[0028] “Oil-soluble” or “oil-dispersible” does not necessarily indicatethat the additives are soluble, dissolvable, miscible or capable ofbeing suspended in the oil of lubricating viscosity, in all proportions.They do mean, however, that they are, for example, soluble or stablydispersible in the oil to an extent sufficient to exert their intendedeffect in the environment in which the oil is employed. Moreover, theadditional incorporation of other additives may also permitincorporation of higher levels of a particular additive, if desired.

[0029] “ppm” means parts per million, expressed by mass based on themass of the lubricating oil composition.

[0030] The abbreviation SAE stands for Society of Automotive Engineers.

[0031] All percentages reported are mass % on an active ingredientbasis, ie., without regard to carrier or diluent oil, unless otherwisestated.

[0032] It should be noted that the lubricating oil compositions of thisinvention comprise defined individual, i.e. separate, components thatmay or may not remain the same chemically before and after mixing. Thus,it will be understood that various components of the composition,essential as well as optional and customary, may react under theconditions of formulation, storage or use, and that the invention alsoprovides the product obtainable or obtained as a result of any suchreaction.

[0033] Also, it should be noted that when the specification refers to alubricating oil composition having a defined amount of sulfated ash,this means that the oil composition gives the defined amount of sulfatedash under ASTM D874.

[0034] The features of the present invention will now be discussed inmore detail.

[0035] Heavy Duty Diesel Engines

[0036] Heavy duty diesel engines according to the present invention arepreferably used in land-based vehicles, more preferably large roadvehicles, such as large trucks. The road vehicles typically have aweight greater than 12 tonnes. The engines used in such vehicles tend tohave a total displacement of at least 6.5, preferably at least 8, morepreferably at least 10, such as at least 15, litres; engines having atotal displacement of 12 to 20 litres are preferred. Generally, engineshaving a total displacement greater than 24 litres are not consideredland-based vehicles. The engines according to the present invention alsohave a displacement per cylinder of at least 1.0 or at least 1.5, suchas at least 1.75, preferably at least 2, litres per cylinder. Generally,heavy duty diesel engines in road vehicles have a displacement percylinder of at most 3.5, such as at most 3.0; preferably at most 2.5,litres per cylinder. The term “heavy duty” in relation to internalcombustion engines is known in the art: see ASTM D4485 at §3.17 whereheavy duty engine operation is characterised by average speeds, poweroutputs and internal temperatures that are generally close to potentialmaximums; therefore, a heavy duty diesel engine is considered to operategenerally under such conditions.

[0037] As used herein, the terms ‘total displacement’ and ‘displacementper cylinder’ are known to those skilled in the art of internalcombustion engines (see “Diesel Engine Reference Book”, edited by B.Challen and R. Baranescu, second edition, 1999, published by SAEInternational). Briefly, the term “displacement” corresponds to thevolume of the cylinder in the engine as determined by the pistonmovement and consequently the “total displacement” is the total volumedependent on the number of cylinders; and the term ‘displacement percylinder’ is the ratio of the total displacement to the number ofcylinders in the engine.

[0038] Lubricating Oil Composition

[0039] The present invention particularly concerns multigradelubricating oil compositions (also known as multigrade lubricants) thattend to be less viscous. The SAE J300 classification defines thelubricants according to their viscometric properties, such as theirmaximum low temperature cranking and pumping viscosities and maximum andminimum kinematic viscosities at 100° C.

[0040] Preferably, the lubricating oil compositions, in each aspect ofthe present invention, have a low temperature cranking viscosity or coldcranking simulated viscosity, independently of the amount of sulfatedash, as measured by ASTM D2602, of less than 6000 mPa.s at −30° C., morepreferably less than 6200 mPa.s at −35° C.

[0041] Preferably, the lubricating oil compositions, in each aspect ofthe present invention, have a sulfated ash, independently of the coldcranking simulated viscosity, as measured by ASTM D874, of less than1.25 or 1.15, more preferably less than any of 1.05, 1.00, and 0.95,such as less than 0.90, especially less than 0.85, advantageously lessthan 0.75, mass %, based on the mass of the oil composition. Thesulfated ash can be in the range from 0 to 0.5 mass %.

[0042] In a preferred embodiment, the amount of sulfated ash, as definedabove, is derived from metal-containing additives only, more preferablythe sulfated ash is derived from metal detergents only, such as acalcium detergent and/or a magnesium detergent.

[0043] Preferably, the lubricating oil compositions, in each aspect ofthe present invention, have a TBN of less than 11.2 or 10.5 or 9.8,preferably less than any one of 9.2, 8.8 and 8.5, especially less than7.8, advantageously less than 7.1. The TBN can be in the range from 2.1to 5.5.

[0044] Preferably, the lubricating oil compositions, in each aspect ofthe present invention, have a metal content, whether transition metal oralkaline earth metal or alkali metal, of less than 4800 or 4400 or 4000,more preferably less than any of 3700, 3500 and 3300, especially lessthan 3000, advantageously less than 2600, ppm. The metal content can bein the in the range from 0 to 1800 ppm.

[0045] Test methods for measuring metal content are well known to thoseskilled in the art.

[0046] In an embodiment of each aspect of the present invention,lubricating oil compositions of the present invention have a maximumkinematic viscosity at 100° C., independently of the cold crankingsimulated viscosity and the amount of sulfated ash, of less than 21.9mm²s; preferably less than 16.3 mm²s; such as less than 12.5 mm²s;especially less than 9.3 mm²s. The kinematic viscosity at 100° C. canbe, for example, in the range of 16.3 to less than 21.9; preferably inthe range of 12.5 to less than 16.3; more preferably in the range of 9.3to less than 12.5; such as in the range of 5.6 to less than 9.3.

[0047] Accordingly, the lubricating oil compositions of the presentinvention are multigrade oil compositions having a viscosmetric grade ofan SAE 10W-X or an SAE 5W-X or 0W-X, where X represents any one of 20,30, 40 and 50, preferably X is 20 or 30 or 40, more preferably Xrepresents 40.

[0048] The American Petroleum Institute (API), Association desConstructeur Europeén d'Autombile (ACEA) and Japanese StandardsOrganisation (JASO) specify the performance level required forlubricating oil compositions. Also there are performance specificationsknown as Global, which contain tests and performance levels from theACEA, API and JASO specifications.

[0049] Thus, a heavy duty lubricating oil composition of the presentinvention preferably satisfies at least the performance requirements ofheavy duty diesel engine lubricants, such as at least the API CG-4;preferably at least the API CH-4; especially at least the API CI-4. Inanother embodiment, the lubricating oil composition of the invention,independently of meeting the API performance requirements, preferablysatisfies, in particular relating to piston cleanliness, at least theACEA E2-96; more preferably at least the ACEA E3-96; advantageously atleast the ACEA E5-99; and especially at least ACEA E4-99. In a furtherembodiment, the lubricating oil composition of the invention,independently of meeting the API and ACEA performance requirements,preferably satisfies the JASO DH-1 or Global DHD-1.

[0050] Oil of Lubricating Viscosity

[0051] The oil of lubricating viscosity is the major liquid constituentof a lubricating oil composition. The oil of lubricating viscosityincludes (a) oil added to a concentrate or additive package, and (b) anyoil present in a concentrate or additive package.

[0052] The oil of lubricating viscosity or lubricating oil can be asynthetic or mineral oil of lubricating viscosity selected from thegroup consisting of Group I, II, III, IV and V basestocks, and a mixturecontaining any two or more thereof.

[0053] Basestocks may be made using a variety of different processesincluding but not limited to distillation, solvent refining, hydrogenprocessing, oligomerization, esterification, and rerefining.

[0054] API 1509 “Engine Oil Licensing and Certification System”Fourteenth Edition, December 1996 states that all basestocks are dividedinto five general categories:

[0055] Group I basestocks contain less than 90% saturates and/or greaterthan 0.03% sulfur and have a viscosity index greater than or equal to 80and less than 120;

[0056] Group II basestocks contain greater than or equal to 90%saturates and less than or equal to 0.03% sulfur and have a viscosityindex greater than or equal to 80 and less than 120;

[0057] Group III basestocks contain greater than or equal to 90%saturates and less than or equal or 0.03% sulfur and have a viscosityindex greater than or equal to 120;

[0058] Group IV basestocks are polyalphaolefins (PAO); and

[0059] Group V basestocks include all other basestocks not included inGroup I, II, III or IV.

[0060] The test methods used in defining the above groups are ASTM D2007for saturates; ASTM D2270 for viscosity index; and one of ASTM D2622,4294, 4927 and 3120 for sulfur.

[0061] Group IV basestocks, i.e. polyalphaolefins (PAO), includehydrogenated oligomers of an alpha-olefin, the most important methods ofoligomerization being free radical processes, Ziegler catalysis,cationic and Friedel-Crafts catalysis.

[0062] Group V basestocks in the form of esters are preferred and arealso commercially available. Examples include polyol esters such aspentaerythritol esters, trimethylolpropane esters and neopentylglycolesters; diesters; C₃₆ dimer acid esters; trimellitate esters, i.e. 1, 2,4-benzene tricarboxylates; and pthalate esters, i.e. 1,2-benzenedicarboxylates. The acids from which the esters are made are preferablymonocarboxylic acids of the formula RCO₂H where R represents a branched,linear or mixed alkyl group. Such acids may, for example, contain 6 to18 carbon atoms

[0063] The oil of lubricating viscosity of the first aspect, andpreferably of the sixth aspect, comprises at least 35 mass % of a GroupIII basestock, based on the mass of the oil of lubricating viscosity,that contains at most 0.03 mass % of sulfur, based on the mass of saidbasestock, and that has a viscosity index of 120 or greater and hasgreater than or equal to 90 mass % saturates, based on the mass of saidbasestock.

[0064] Preferably, the oil of lubricating viscosity comprises saidbasestock in an amount of at least 40, more preferably at least 45, suchas at least 50, especially in the range of 55 to 95, advantageously from65 to 90, for example 70 to 80 or 85, mass %, based on the mass of theoil of lubricating viscosity. For the avoidance of doubt, the oil oflubricating viscosity includes the basestock that arise from theprovision of additive components in the oil composition.

[0065] In a preferred embodiment, the defined proportion of saidbasestock is that added to the concentrate or additive package.

[0066] In the instance the oil of lubricating viscosity comprises amixture of basestock Groups, it is preferred that a Group I basestockand a Group III basestock are present.

[0067] In a preferred embodiment, the oil of lubricating viscosityconsists essentially of a Group III basestock and one or more of a GroupIV basestock and a Group V basestock in the form of an ester, andoptionally a minor amount of those basestocks that arise from theprovision of additive components in the oil composition.

[0068] Additive Composition

[0069] In each aspect of the present invention, an additive compositioncomprises a detergent composition and one or more other additives, whichmay include other metal-containing additives, such as zincdithiophosphates.

[0070] A detergent composition contains a detergent. A detergent is anadditive that reduces formation of piston deposits, for examplehigh-temperature varnish and lacquer deposits, in engines; it hasacid-neutralising properties and is capable of keeping finely dividedsolids in suspension. It is based on metal “soaps”, that is metal saltsof organic acids, also known as surfactants herein.

[0071] A detergent comprises a polar head, e.g. the metal salt of theorganic acid, with a long hydrophobic tail for oil solubility.Therefore, the organic acids typically have one or more functionalgroups, such as OH or COOH or SO₃H; and a hydrocarbyl substituent.

[0072] Examples of organic acids include sulfonic acids; phenols,salicylic acids and sulfurised derivatives thereof; and carboxylicacids.

[0073] The detergents of the present invention can comprise metal saltsof an organic acid and particles of basic inorganic salts (e.g. calciumcarbonate particles).

[0074] Thus, each or the metal detergent in the detergent compositionmay be neutral or overbased, such terms are understood by those skilledin the art.

[0075] A detergent composition comprising one or more metal salts oforganic acids may be present, for example, a mixture of metal sulfonateand metal phenate.

[0076] The detergents of the present invention may be salts of one typeof organic acid or salts of more than one type of organic acids, forexample hybrid complex detergents. Preferably, they are salts of onetype of organic acid.

[0077] A hybrid complex detergent is where the basic material within thedetergent is stabilised by more than one type of organic acid. It willbe appreciated by one skilled in the art that a single type of organicacid may contain a mixture of organic acids of the same type. Forexample, a sulfonic acid may contain a mixture of sulfonic acids ofvarying molecular weights. Such an organic acid composition isconsidered as one type. Thus, complex detergents are distinguished frommixtures of two or more separate overbased detergents, an example ofsuch a mixture being one of an overbased calcium salicylate detergentwith an overbased calcium phenate detergent.

[0078] The art describes examples of overbased complex detergents. Forexample, International Patent Application Publication Nos.97-46643/4/5/6 and 7 describe hybrid complexes made by neutralising amixture of more than one acidic organic compound with a basic metalcompound, and then overbasing the mixture. Individual basic micelles ofthe detergent are thus stabilised by a plurality of organic acid types.Examples of hybrid complex detergents include calciumphenate-salicylate-sulfonate detergent, calcium phenate-sulfonatedetergent and calcium phenate-salicylate detergent.

[0079] EP-A-O 750 659 describes a calcium salicylate phenate complexmade by carboxylating a calcium phenate and then sulfurising andoverbasing the mixture of calcium salicylate and calcium phenate. Suchcomplexes may be referred to as “phenalates”

[0080] Preferred complex detergents are salicylate-based detergents, forexample, a calcium phenate-salicylate-sulfonate detergent and“phenalates”.

[0081] A detergent, whether a complex or not, can have a Total BaseNumber (TBN) in the range of 15 or 60 to 600, preferably 100 to 450,more preferably 160 to 400.

[0082] For the avoidance of doubt, the detergent composition may alsocomprise ashless detergents, i.e. non-metal containing detergents.

[0083] Preferably the detergent composition comprises at least oneoverbased metal detergent.

[0084] Group 1 and Group 2 metals are preferred as metals in thedetergents; more preferably calcium and magnesium, especially preferredis calcium.

[0085] Preferably, the amount of alkaline earth metal in the lubricatingoil composition, in each aspect of the invention, is less than 3200, or3000 or 2800, more preferably less than any of 2500, 2400 and 2300,especially less than 2000, advantageously less than 1800, ppm. Thealkaline earth metal content can be in the range from 0 to 1200 ppm.

[0086] Preferably, the detergent composition is present in the oilcomposition, in each aspect of the invention, in an amount, based onsurfactant content, of at most 50, preferably at most 30, especially atmost 20, millimoles of surfactant per kilogram of the oil composition(mmol/kg). In an embodiment, the amount of detergent composition, basedon surfactant content, in the oil composition is 10 tol5 mmol/kg.

[0087] Means for determining the amount of surfactant are known to thoseskilled in the art. For example, a skilled person can calculate theamounts in the final lubricating oil composition from informationconcerning the amount of raw materials (e.g., organic acids) used tomake the detergent(s) and from information concerning the amount ofdetergent(s) used in the final oil composition. Analytical methods(e.g., dialysis, metal analysis, CO2 analyis, potentiometric titrationand chromatography) can also be used to determine the amounts ofsurfactant.

[0088] It will be appreciated by a skilled person in the art that themethods to determine the amount of metal salts of organic acids (alsoknown as surfactants) are at best approximations and that differingmethods will not always give exactly the same result; they are, however,sufficiently precise to allow the practice of the present invention.

[0089] Co-additives

[0090] Other additives may also be present in the oil composition of thepresent invention.

[0091] Co-additives suitable in the present invention include viscosityindex improvers, corrosion inhibitors, oxidation inhibitors orantioxidants, dispersants, rust inhibitors or rust prevention agents,anti-wear agents, pour point depressants, demulsifiers, and anti-foamingagents.

[0092] Viscosity index improvers (or viscosity modifiers) impart highand low temperature operability to a lubricating oil and permit it toremain shear stable at elevated temperatures and also exhibit acceptableviscosity or fluidity at low temperatures. Suitable compounds for use asviscosity modifiers are generally high molecular weight hydrocarbonpolymers, including polyesters, such as polymethacrylates;poly(ethylene-co-propylene) polymers and closely related modifications(so called olefin copolymers); hydrogenated poly(styrene-co-butadiene or-isoprene) polymers and modifications; and esterifiedpoly(styrene-co-maleic anhydride) polymers . Oil-soluble viscositymodifying polymers generally have number average molecular weights of atleast 15,000 to 1,000,000, preferably 20,000 to 600,000, as determinedby gel permeation chromatography or light scattering methods. Thedisclosure in Chapter 5 of “Chemistry & Technology of Lubricants”,edited by R. M. Mortier and S. T. Orzulik, First edition, 1992, BlackieAcademic & Professional, is incorporated herein.

[0093] Corrosion inhibitors reduce the degradation of metallic partscontacted by the lubricating oil composition. Thiadiazoles, for examplethose disclosed in U.S. Pat. Nos. 2,719,125, 2,719,126 and 3,087,932 areexamples of corrosion inhibitors for lubricating oils.

[0094] Oxidation inhibitors, or antioxidants, reduce the tendency ofmineral oils to deteriorate in service, evidence of such deteriorationbeing, for example, the production of varnish-like deposits on metalsurfaces and of sludge, and viscosity increase. Suitable oxidationinhibitors include sulfurized alkyl phenols and alkali or alkaline earthmetal salts thereof; hindered phenols; diphenylamines;phenyl-naphthylamines; and phosphosulfurized or sulfurized hydrocarbons.

[0095] Other oxidation inhibitors or antioxidants which may be used inlubricating oil compositions include oil-soluble copper compounds. Thecopper may be blended into the oil as any suitable oil-soluble coppercompound. By oil-soluble it is meant that the compound is oil-solubleunder normal blending conditions in the oil or additive package. Thecopper may, for example, be in the form of a copper dihydrocarbyl thio-or dithio-phosphate. Alternatively, the copper may be added as thecopper salt of a synthetic or natural carboxylic acid, for example, a C₈to C₁₈ fatty acid, an unsaturated acid, or a branched carboxylic acid.Also useful are oil-soluble copper dithiocarbamates, sulfonates,phenates, and acetylacetonates. Examples of particularly useful coppercompounds are basic, neutral or acidic copper Cu^(I) and/or Cu^(II)salts derived from alkenyl succinic acids or anhydrides.

[0096] Copper antioxidants will generally be employed in an amount offrom about 5 to 500 ppm by weight of the copper, in the finallubricating composition.

[0097] Dispersants maintain oil-insoluble substances, resulting fromoxidation during use, in suspension in the fluid, thus preventing sludgeflocculation and precipitation or deposition on metal parts. So-calledashless dispersants are organic materials which form substantially noash on combustion, in contrast to metal-containing (and thusash-forming) detergents. Borated metal-free dispersants are alsoregarded herein as ashless dispersants. Suitable dispersants include,for example, derivatives of long chain hydrocarbyl-substitutedcarboxylic acids, in which the hydrocarbyl group has a number averagemolecular weight tends of less than 15,000, such as less than 5000;examples of such derivatives being derivatives of high molecular weighthydrocarbyl-substituted succinic acid. Such hydrocarbyl-substitutedcarboxylic acids may be reacted with, for example, a nitrogen-containingcompound, advantageously a polyalkylene polyamine, or with an alcohol.Particularly preferred dispersants are the reaction products ofpolyalkylene amines with alkenyl succinic anhydrides. Examples ofspecifications disclosing dispersants of the last-mentioned type areU.S. Pat. No. 3,202,678, 3,154,560, 3,172,892, 3,024,195, 3,024,237,3,219,666, 3,216,936 and BE-A-662 875.

[0098] Heavy duty diesel engine lubricating oil compositions tend tohave a higher amount of nitrogen, preferably derived from a dispersant,than passenger car engine oil compositions because more oil-insolublesubstances, such as soot, are formed in heavy duty diesel engines.Accordingly, the nitrogen content, is preferably at least 0.06, morepreferably at least 0.08, such as at least 0.10, especially at least0.12, mass %, based on the mass of the oil composition. The amount ofnitrogen, preferably derived from the dispersant, tends not to be morethan 0.2 mass %. The amount of nitrogen is measured according to ASTMD4629.

[0099] Alternatively or in addition, dispersancy may be provided bypolymeric compounds capable of providing viscosity index improvingproperties and dispersancy, such compounds are known as amultifunctional viscosity index improvers. Such polymers differ fromconventional viscosity index improvers in that they provide performanceproperties, such as dispersancy and/or antioxidancy, in addition toviscosity index improvement.

[0100] Dispersant olefin copolymers and dispersant polymethacrylates areexamples of multifunctional viscosity index improvers. Multifunctionalviscosity index improvers are prepared by chemically attaching variousfunctional moieties, for example amines, alcohols and amides, ontopolymers, which polymers preferably tend to have a number averagemolecular weight of at least 15,000, such in the range from 20,000 to600,000, as determined by gel permeation chromatography or lightscattering methods. The polymers used may be those described above withrespect to viscosity modifiers. Therefore, amine molecules may beincorporated to impart dispersancy and/or antioxidancy characteristics,whereas phenolic molecules may be incorporated to improve antioxidantproperties. A specific example, therefore, is an inter-polymer ofethylene-propylene post grafted with an active monomer such as maleicanhydride and then derivatized with, for example, an alcohol or amine.

[0101] EP-A-24146 and EP-A-0 854 904 describe examples of dispersantsand dispersant viscosity index improvers, which are accordinglyincorporated herein.

[0102] Rust inhibitors selected from the group consisting of nonionicpolyoxyalkylene polyols and esters thereof, polyoxyalkylene phenols, andanionic alkyl sulfonic acids may be used.

[0103] Antiwear agents, as their name implies, reduce wear of metalparts. Zinc dihydrocarbyl dithiophosphates (ZDDPs) are very widely usedas antiwear agents. Examples of ZDDPs for use in oil-based compositionsare those of the formula Zn[SP(S)(OR¹)(OR²)]₂ wherein R¹ and R² containfrom 1 to 18, and preferably 2 to 12, carbon atoms.

[0104] Sulfur- and molybdenum-containing compounds are also examples ofanti-wear additives. Also suitable are ashless phosphorus- andsulfur-containing compounds.

[0105] Pour point depressants, otherwise known as lube oil flowimprovers, lower the minimum temperature at which the fluid will flow orcan be poured. Such additives are well known. Foam control may beprovided by an antifoamant of the polysiloxane type, for example,silicone oil or polydimethyl siloxane.

[0106] A small amount of a demulsifying component may be used. Apreferred demulsifying component is described in EP-A-0 330 522. It isobtained by reacting an alkylene oxide with an adduct obtained byreacting a bis-epoxide with polyhydric alcohol.

[0107] Some of the above-mentioned additives may provide a multiplicityof effects; thus for example, a single additive may act as adispersant-oxidation inhibitor. This approach is well known and need notbe further elaborated herein.

[0108] Preferably an anti-wear additive, such a metaldihydrocarbyidithiophosphate, for example, zincdihydrocarbyldithiophosphate, is present in the lubricating oilcompositions of the present invention.

[0109] When lubricating compositions contain one or more of theabove-mentioned additives, including the detergents, each additive istypically blended into the base oil in an amount which enables theadditive to provide its desired function. Representative effectiveamounts of such additives, when used in lubricants, are as follows: Mass% a.i.* Mass % a.i.* Additive (Broad) (Preferred) Viscosity Modifier0.01-6 0.01-4 Corrosion Inhibitor 0.01-5   0.01-1.5   OxidationInhibitor 0.01-5   0.01-1.5  Friction Reducer 0.01-5   0.01-1.5 Dispersant 0.1-20  0.1-8  Dispersant Viscosity Modifier 0.01-5  0.05-5   Detergent 0.01-6   0.01-3   Anti-wear Agent 0.01-6   0.01-4  Pour Point Depressant 0.01-5   0.01-1.5  Rust Inhibitor 0.001-0.5 0.01-0.2  Anti-Foaming Agent 0.001-0.3  0.001-0.15  Demulsifier0.001-0.5  0.01-0.2 

[0110] The additives may be incorporated into an oil of lubricatingviscosity (also known as a base oil) in any convenient way. Thus, eachadditive can be added directly to the oil by dispersing or dissolving itin the oil at the desired level of concentration. Such blending mayoccur at ambient temperature or at an elevated temperature. Typically anadditive is available as an admixture with a base oil so that thehandling thereof is easier.

[0111] When a plurality of additives are employed it may be desirable,although not essential, to prepare one or more additive packages (alsoknown as additive compositions or concentrates) comprising additives anda diluent, which can be a base oil, whereby the additives, with theexception of viscosity modifiers, multifuntional viscosity modifiers andpour point depressants, can be added simultaneously to the base oil toform the lubricating oil composition. Dissolution of the additivepackage(s) into the oil of lubricating viscosity may be facilitated bydiluent or solvents and by mixing accompanied with mild heating, butthis is not essential. The additive package(s) will typically beformulated to contain the additive(s) in proper amounts to provide thedesired concentration in the final formulation when the additivepackage(s) is/are combined with a predetermined amount of oil oflubricating viscosity. Thus, one or more detergents may be added tosmall amounts of base oil or other compatible solvents (such as acarrier oil or diluent oil) together with other desirable additives toform additive packages containing from 2.5 to 90, preferably from 5 to75, most preferably from 8 to 60, mass %, based on the mass of theadditive package, of additives on an active ingredient basis in theappropriate proportions. The final formulations may typically contain 5to 40 mass % of the additive package(s), the remainder being oil oflubricating viscosity.

[0112] The amount of additives in the final lubricating oil compositionis generally dependent on the type of the oil composition, for example,a heavy duty diesel engine lubricating oil composition has 2 to 20,preferably 5 to 18, more preferably 7 to 16, such as 8 to 14, mass % ofadditives, based on the mass of the oil composition.

[0113] Thus, a method of preparing the oil composition according to thepresent invention can involve admixing an oil of lubricating viscosityand one or more additives or an additive package that comprises one ormore of the additives.

[0114] A means of increasing the power output of an engine, particularlya compression-ignited engine, is to include a turbocharger in itsassembly. The turbo-charger enables more fuel to be burnt per givencylinder size by pressurising the intake air so that more air is chargedto the cylinder.

[0115] Turbo-chargers are typically powered by the gas expelled throughthe exhaust, and this can lead to a loss of efficiency of theturbo-charger during the life-time of the engine because speciescontained in the exhaust gas deposit within the turbo-charger. It hasbeen also discovered that lubricating oil compositions of the presentinvention can minimise the loss of efficiency of a turbo-charger. Amethod of determining the loss of efficiency is, for example, theOM441LA test, where a boost pressure loss, as a percent, is given: thehigher the boost pressure loss the greater the loss of efficiency.

EXAMPLES

[0116] Lubricating oil compositions, identified herein as Examples A toD and Examples 1 to 4, were blended by methods known in the art atcomparable TBN from oils of lubricating viscosity and additiveconcentrates. Examples A to D are comparative and Examples 1 to 4 are ofthe invention. Table 1 shows details of the oil of lubricating viscosityused and the physical properties of the resulting oil compositions.Comparative Example A was blended to a SAE 15W40 viscometric grade,whereas comparative Examples B to D and Examples 1 to 4 were blended toan SAE 10W40 viscometric grade.

[0117] Comparative Examples A to D and Examples 1 to 4 were tested forpiston cleanliness and boost pressure loss in the OM441LA test,according to the CEC-L-52-T-97 procedure. The results are also given inTable 1.

[0118] Table 1 shows that Example A, a SAE 15W40 lubricating oilcomposition, provided better piston cleanliness and boost pressure lossthan Example B, an oil composition containing the same additives asthose in Example A but blended to a SAE 10W40 viscometric grade.

[0119] Further, the results in Table 1 show that the piston cleanlinessand boost pressure loss are improved as the proportion of Group IIIbasestock is increased in an SAE 10W40 oil composition (see Example Bthrough to Example 4).

[0120] ACEA E5-99 performance specification sets a passing limit of atleast 25 merits points for piston cleanliness and at most 4% for boostpressure loss. Accordingly, at least about 35 mass % of a Group IIIbasestock in an oil of lubricating viscosity may be required to meet thelimits set by ACEA E5-99 in respect of the piston cleanliness and boostpressure loss. TABLE 1 Example A Example B Example C Example D Example 1Example 2 Example 3 Example 4 Oil of lubricating viscosity Group 1basestock, mass % 100 100 67 67 56 33 33 24 Group III basestock, mass %0 0 33 33 44 67 67 76 Physical characteristics SAE J300 classification15W40 10W40 10W40 10W40 10W40 10W40 10W40 10W40 Sulfated ash, mass %1.06 1.06 1.04 1.09 1.10 1.08 1.10 1.10 Phosphorus, mass % 0.092 0.0960.085 0.098 0.120 0.098 0.098 0.097 TBN 9.3 9.3 9.3 9.5 10.1 9.5 9.7 9.8OM441LA Results Piston cleanliness, merits 26.0 12.7 21.8 14.5 30.2 31.632.8 29.7 Boost pressure loss at 400 hrs., % 2.7 38.9 19.1 1.5 2.1 −2.8−1.2 −1

1. A heavy duty diesel engine lubricating oil composition comprising, ormade by admixing: (A) a major amount of an oil of lubricating viscositycomprising at least 35 mass % of a Group III basestock, based on themass of the oil of lubricating viscosity, that contains at most 0.03mass % of sulfur, based on the mass of said basestock, and that has aviscosity index of 120 or greater and has greater than or equal to 90mass % saturates, based on the mass of said basestock; and (B) a minoramount of an additive composition comprising: (i) a detergentcomposition; and (ii) one or more other additives; wherein the oilcomposition has a cold cranking simulated viscosity, measured accordingto ASTM D2602, of less than 7000 mPa.s at −25° C. and a sulfated ashcontent, measured according to ASTM D874, of less than 1.35 mass %,based on the mass of the oil composition.
 2. The oil compositionaccording to claim 1 wherein the oil of lubricating viscosity consistsessentially of a Group III basestock and one or more of a Group IVbasestock and a Group V basestock in the form of an ester.
 3. The oilcomposition according to claim 1 wherein the detergent compositioncomprises a magnesium detergent additive and/or a calcium detergentadditive.
 4. The oil composition according to claim 3 further comprisinga zinc dihydrocarbyl dithiophosphate additive.
 5. A method oflubricating a heavy duty diesel engine, which engine has a totaldisplacement of at least 6.5 litres and a displacement per cylinder ofat least 1.0 litre per cylinder, which method comprises supplying to theengine a lubricating oil composition as defined in claim
 1. 6. Acombination of a heavy duty diesel engine, which engine has a totaldisplacement of at least 6.5 litres and a displacement per cylinder ofat least 1.0 litre per cylinder and a lubricating oil composition asdefined in claim
 1. 7. A method of improving the piston cleanliness ofan engine, which method comprises lubricating the engine with alubricating oil composition as defined in claim
 1. 8. A heavy dutydiesel engine lubricating oil composition giving at least 25 pistoncleanliness merit points and not greater than 4% boost pressure loss inthe OM441LA engine test, according to the CEC-L-52-T-97 procedure, whichoil composition comprises, or is made by admixing: (A) a major amount ofan oil of lubricating viscosity; and (B) a minor amount of an additivecomposition comprising: (i) a detergent composition; and (ii) one ormore other additives; wherein the oil composition has a cold crankingsimulated viscosity, measured according to ASTM D2602, of less than 7000mPa.s at −25° C. and a sulfated ash content, measured according to ASTMD874, of less than 1.35 mass %, based on the mass of the oilcomposition.